There is no set age u could be few months old or years old, it's about parents deciding their child is joining Gods family so to speak then later in life that child can make their own mind and confirm their belief thru confirmation.
My DD's were both 14 months at the time and at DD2's she was youngest child there.
They had 3 being done on the day, the vicar gave nice talk on the meaning and history behind it, he really got all the kids involved he was great.
Afterwards we had a BBQ at home, usually the church asks for a donation rather than a fee for the service.
Call up your church, they will be more than happy to answer anything.
Oh and there is also the important task of choosing god parents.